Abrasive element dimension sensing mechanism

ABSTRACT

A transducer feedback mechanism for sensing the precise position of a rotating abrasive element and moving it towards or away from a workpiece to compensate for a change in radius due to wear or expansion. The sensing device includes a carbide pad in engagement with the grinding surface of the abrasive element, in radial alignment with the center thereof, and any movement of the pad causes a sensing transducer to signal a servo-amplifier or computer which controls the position of the element relative to the workpiece. Since the sensing pad is itself subject to wear, means are also provided to periodically re-zero the sensing transducer to compensate for such wear.

United States Patent Schaller 51 Sept. 19, 1972 Schaller ..51/238 RSchaller et a1. ..51/135 R Primary Examinerl-larold D. WhiteheadAttorney-Bruns & Jenney [57] ABSTRACT A transducer feedback mechanismfor sensing the precise position of a rotating abrasive element andmoving it towards or away from a workpiece to compensate for a change inradius due to wear or expansion. The sensing device includes a carbidepad in en gagement with the grinding surface of the abrasibe element, inradial alignment with the center thereof, and any movement of the padcauses a sensing transducer to signal a servo-amplifier or computerwhich controls the position of the element relative to the workpiece.Since the sensing pad is itself subject to wear, means are also providedto periodically re-zero the sensing transducer to compensate for suchwear.

11 Claims, 6 Dnwing Figures [72] Inventor: Robert L. Schaller, Syracuse,N.Y.

[73] Assignee: Sundstrand-Engelberg, Inc., Liverpool, N.Y.

[22] Filed: Nov. 23, 1970 [21] Appl. No.: 91,636

[52] US. Cl. ..5l/l65.88, 51/103 R, 51/135 R [51] Int. Cl. ..B24b 49/00[58] Field of Search ..5l/165.88, 165.87, 103 R, 135 R [56] ReferencesCited UNITED STATES PATENTS 980,164 12/1910 Nichols ..51/165.881,549,600 8/1925 Mueller ..5l/l65.88 2,647,347 8/1953 Blanchette..51/103 R X 3o l Y IO X 2| 2 PATENTEBssmmz 3,691,698

sum 2 BF 3 ROBERT L. SCHALLER INVENTOR.

P'A'TE'N'TEDSEP 19 I972 SHEET 3 [1F 3 INVENTOR. ROBERT L. SCHALLERABRASIVE ELEMENT DIMENSION SENSING MECHANISM BACKGROUND OF THE INVENTIONThis invention relates generally to grinding machinery, and hasparticular reference to a novel mechanism for sensing the preciseposition of a rotating abrasive element.

As is well known in the art, abrasive elements used in grindingconstantly undergo changes in the radial dimension due to wear, heatand, in the case of an abrasive belt, centrifugal force acting on thebelt and the soft covering on the contact wheel. Such variations, ofcourse, affect the accuracy of the grinding operation and to offsetthis, sensing devices have been developed to detect the variations andthen move the abrasive element relative to the workpiece the distancerequired to compensate.

Heretofore, the sensing devices have generally been in the form ofhardened pads which ride on the surface of the abrasive element or fluidtype sensors which have the advantage that the sensing fluid is notitself subject to wear. The contacting pads, even though provided with alubricant, are subject to wear and in most devices means are notprovided to accurately adjust for such wear which introduces an error inthe abrasive element variations detected by the sensor. This, of course,is undesirable where very close tolerances are required in theworkpiece. The fluid type sensors, on the other hand, have not proved tobe a complete solution to the problem since, by the very nature of thesensing medium, they are subject to inaccuracies that may be detrimentalto precision grinding.

SUMMARY OF THE INVENTION In the present invention the sensing mechanismis particularly adapted for use with centerless and cam grinders whereinthe abrasive element support is movable linearly towards or away from aworkpiece, the center of which always coincides with a predetermined,fixed centerline. The sensing member is a hardened pad in engagementwith the abrasive element operating surface and mounted for linearmovement along a radius of the abrasive element. The sensing pad formsthe extremity of a precision transducer device that is pre-set to a zeroreference point, and any movement of the pad due to variations in theradius of the abrasive element causes a deviation from the zeroreference point in the transducer. These deviations are transmittedelectronically to precision movement actuating means for the abrasiveelement support whereby the latter is moved relative to the workpiece tocompensate for the change in radius that has been detected.

To solve the problem of wear on the sensing pad which can introduceerror in the readings of the transducer, the invention provides atransducer zero reset mechanism in the form of a pad wear indicator.This comprises a fixed reference surface that is totally independent ofthe abrasive element and with which the sensing pad is initially broughtinto contact to establish the transducer zero reference point.Thereafter, in the course of the grinding operation, the sensing pad isperiodically brought into contact with the reference surface and anywear on the pad will show as a deviation from the zero reference pointenabling the transducer device to be re-zeroed in accord therewith.

2 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially diagrammaticside elevation, with parts being shown in section, of a centerlessgrinder and sensing mechanism of the invention;

FIG. 2 is a horizontal section taken on line 2-2 of FIG. 1;

FIG. 3 is an enlarged side elevation of the sensing mechanism of FIG. 1with certain parts shown in section to better illustrate theconstruction and arrangement of the parts;

FIG. 4 is an enlarged front elevation of the sensing mechanism; and

FIGS. 5 and 5A are diagrammatic illustrations to show how the sensingmechanism can be moved transversely with respect to the abrasiveelement, to different points across its width, in straight and curvedsurface grinding operations, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENT.

With reference to FIG. 1 of the drawings, 10 indicates a workpiece suchas a bar or tube, 11 is the regulating wheel and 12 is the contact wheelof a centerless grinding machine. The contact wheel is motor driven in aconventional manner and carries an abrasive belt 14 which also passesover an idler pulley 15. The sensing mechanism to be described can beused with either a disc or belt type abrasive element but because thesensing problems are more difficult with a belt, the description will bedirected to a machine in which an abrasive belt is employed.

The contact wheel 12 and idler 15 are mounted in a grinding column 16forming a part of the grinding head, generally indicated by thereference number 17. The grinding head includes a sub-base 18 containinga set of ways (not shown) by means of which the head can be movedlinearly towards or away from the workpiece 10 along the horizontalcenter line 19. A plate 20 supports the grinding column 16 and ispivotally connected to the sub-base at 21 to permit the grinding elementto be moved angularly with respect to the workpiece for a purpose to bedescribed hereinafter. In this connection, it will be seen that the axisof the pivot 21 is in vertical alignment with the center of the contactwheel 12.

To accommodate workpieces of different diameters, the regulating wheel 11, as well as the grinding head 17 can be moved linearly along thehorizontal center line 19 by conventional means. Similarly, the workrest blades (not shown) are movable as a single unit along a linear pathdisposed at an oblique angle to the vertical line 22 through the centerof the workpiece. For a detailed description of the work restpositioning means, reference may be had to US. Pat. No. 3,466,810granted Sept. 16, 1969 to the applicant herein.

The sub-base 18 on which the grinding head 17 is mounted can be movedtoward or away from the workpiece by means of a precision ball screw 24and nut 25. Movement actuating mechanisms of this type have developed tosuch a degree that they are capable of accurate positioning within atenth of a thousandth of an inch. Accordingly, the distance X in FIG. 1,which is the distance between the centers of the workpiece and contactWheels, can be very accurately controlled as by a computer or otherelectronic means. In this connection, it should be noted that incenterless grinders of the type disclosed herein the vertical centerline 22 through the center of the workpiece is a predetermined passlinewith reference to which all movable grinding components are positionedin a linear manner.

The distance from the center of the contact wheel 12 to the operatingsurface of the abrasive belt 14, designated R in FIG. 1, is aspreviously noted subject to variations due to wear, centrifugal force orother factors. This in turn affects the dimension Y, which is thedistance between the belt surface and workpiece center, and thus affectsthe accuracy of the grinding operation. The relationship of X, R and Ycan be expressed by the formula Y X R, where Y is the dimension thatshould be held constant in any given grinding operation to maintainuniformity.

To keep dimension Y constant, it is necessary to determine exactly whatthe variable dimension R is at all times and feed this information backto the grinding head positioning means whereby the distance X is changedto compensate for variations in R. The information as to R variationscan be fed back to a servoamplifier or computer (not shown), which donot per se play a part of the present invention, and provide a signal toa positioning motor 26 which actuates the ball screw 24 to move thegrinding head 17 linearly towards or away from the workpiece. The exactposition of the grinding head at any time is determined by a positioningread-out transducer 27 of a known type.

Having reference now to FIG. 3, it will be seen that the contact wheel12 is provided with a covering 28 over which the abrasive belt 14passes, the covering being of a resilient material such as polyurethaneor neoprene. The factors which cause variations in the dimension Rinclude the expansion of this covering due to heat, high speedcentrifugal forces which tend to throw the belt outwardly and the wearthat occurs on the belt itself, particularly in the first few minutes ofdirect use. In accord with the invention, these dimensional variationsare sensed by a sensing member 29 which is centered on a radius of thecontact wheel and is movable linearly along that radius with changes inthe dimension R.

The sensing member 29, shown in retracted position in FIGS. 3 and 4, ispreferably a carbide pad that in operation is held in contact with thebelt surface by a light spring force (not shown). The carbide pad iswell adapted to withstand the abrasiveness of the abrasive element, andwear on the pad is reduced to some extent by a coolant which alsoprovides lubrication.

The pad 29 forms the outer extremity of a transducer device 30 which, inthe embodiment of the invention disclosed, is a commercially availablelinear variable differential transformer. In this highly sensitivedevice, the sensing pad is operatively connected to an iron slugpositioned in a magnetic field within the transducer, and any change inthe position of the pad is reflected by the slug which results in achange in the output signal of the transducer. The transducer output isfed back through electronic means to the grinding head position ingmotor 26, as indicated above. When in belt contacting position, thesensing pad passes through a bore 31 in a guard member 32, the latterbeing provided to protect the delicate transducer device against damagedue to belt breakage or a similar mishap.

The transducer device 30, which can accurately sense a dimensionalchange of up to a half inch, is

secured by a pair of brackets 34 to a slide 35. In setting I up theapparatus, the transducer is mechanically positioned in approximatelycorrect operating position, secured in place by tightening the bracketbolts 36 and then any further adjustment that is necessary is madeelectronically. Should the electronic adjustments go beyond the capacityof the transducer, it is only necessary to loosen the bracket bolts andmake a further mechanical adjustment.

The transducer carrying slide 35 is reciprocably movable on ways 37which form a part of a second slide 38, and the slide assembly indisposed so that the axis of the transducer is colinear with a radius 39of the contact wheel and movement of the sensing pad 29 is linear onthis radius. Movement of slide 35 is effected by a precision ball screw40 and nut 41, the ball screw being driven by an in-feedservo-controlled motor 42. The exact position of the slide at any timeis determined by a resolver or positioning read-out transducer 44.

The second slide 38 is reciprocably movable on ways disposed at rightangles to the ways 37 whereby slide 38 permits movement of the sensingmechanism transversely with respect to the abrasive belt. The ways 45form a part of a bracket 46 that is secured to the grinding column 16 bybolts 47. Like the slide 35, movement of slide 38 is effected by aprecision ball screw and nut 48, 49 with the screw being actuated by acontrol motor 50, FIG. 4, similar to motor 42 and the exact position ofthe slide being determined by a resolver transducer 51.

In order to accurately detect variations in the R dimension, it isnecessary to set the transducer device 30 to a zero reference or nullpoint. This can be accomplished by moving a new carbide pad into contactwith a new abrasive belt while the latter is stationary on the contactwheel. This will position the iron slug at a particular point in thetransducer magnetic field and will give a reading that will be the zeroreference point. Thereafter, with the apparatus performing a grindingoperation, any increase in the R dimension due to heat expansion orcentrifugal force or any decrease in R due to belt wear will result incorresponding movement by the sensing pad and slug, and movement of thelatter away from the zero reference point in either direction will besensed by the transducer which will signal the grinding head positioningmotor 26 as previously described.

However, the carbide pad 29 is also subject to wear, and as this wearoccurs the pad will move closer to the center of the contact wheelcausing a deviation from the zero reference point entirely independentof deviations caused by changes in the R dimension. This, of course,introduces an error in the signals that are fed back to the controlmotor 26 and thus affects the accuracy of the grinding operation. Tosolve this problem, the sensing mechanism of the invention is providedwith means for detecting wear on the sensing pad and for resetting thezero reference point should this be necessary.

The sensing pad wear detecting mechanism includes a pin 52, FIG. 3, theouter end of which is guided for reciprocable movement by a bushing 54inthe slide 38. The inner end of the pin terminates in a piston 55 locatedin a cylinder assembly 56 secured to the back of slide 38. By means ofan air inlet passage 57, air can be admitted to drive the piston to theopposite end of the cylinder, against the bias of spring 58, whereby pin52 is thrust out into the path of the previously retracted sensing pad.

The pin 52, which in projected position provides a fixed referencesurface totally independent of the belt and contact wheel, will beinitially projected when it is known that there is no wear on thesensing pad and the pad brought into engagement therewith. This willgive a transducer reading that can be recorded as the sensing pad nullpoint. After a period of grinding, during which pin 52 is retracted, thesensing pad can again be brought into engagement with the pin, and anywear on the pad will show as a deviation from its null point. The zeroreference point for the transducer will then be changed by the amount ofthis deviation (re-set) so that the wear on the sensing pad is not afactor in the variations it detects in the dimension R. Since the wearon the pad is normally very small and is checked frequently, thepossibility of consequential error due to such wear is negligible.

After each use of the pin 52 to detect wear on the sensing pad, the airin the cylinder is allowed to escape and spring 58 moves piston 55 andthe pin back into their normal, retracted position. A second pin 59,which projects from the piston on its side opposite pin 52, passesthrough the end wall of the cylinder and engages a microswitch 60 whenpin 52 is retracted. The microswitch is connected by simple circuitry toan interlock (not shown) which prevents movement of the sensing pad intocontact with the abrasive belt if pin 52 is in its outwardly projectingposition.

In FIG. 5 there is a diagrammatic illustration of the manner in whichthe sensing mechanism can be moved transversely with respect to theabrasive belt 14 to points such as A, B, C, D and Eby means of slide 38,FIGS. 3 and 4, and its previously described movement actuating means. Inaddition, the plate 20, FIG. 1, can be pivoted about its pivot point 21to permit the grinding element to be moved angularly with respect to theworkpiece, such movement being actuated by a precision ball screw 61 inmesh with an arcuate rack 62 on the plate. The ball screw is driven byan angle positioning motor 64, and the exact angular position of theplate at any time is determined by an angle position transducer 65. Withthe grinding head being pivotally moved in this manner, as for exampleto grind cams or large paper mill rolls, it is very important to sensethe grinding element at the exact point at which the grind occurs. Thiscan be accomplished by moving the sensing mechanism to points such asare indicated at A, B, C, D and E in FIG. 5A by means of slide 38 andits movement actuating means.

In their present state of development, the seam or joint in mostcontinuous abrasive belts is no thicker than the belt itself. However,if the seam were thicker, it could cause the transducer to give a falsesignal and in such a situation the invention contemplates the provisionof circuitry to nullify transducer signals of very short duration.

From the foregoing description, it will be apparent that the inventionprovides a novel and very useful mechanism for sensing the preciseposition of a rotating abrasive element. As will be understood by thosefamiliar with the art, the invention may be embodied in other specificforms without departing from the spirit or essential characteristicsthereof.

I claim:

1. A mechanism for sensing the dimension of a rotating abrasive elementmovable linearly toward and from a workpiece comprising a sensing memberin contact with the abrasive element, the sensing member forming a partof a transducer device initially set to a zero reference point, thesensing member being moved radially of the abrasive element upon anychange in the radial dimension thereof, said movement causing adeviation from the zero reference point in the transducer device,circuit means responsive to the transducer device deviations to move theabrasive element linearly relative to the workpiece to compensate forthe i change in radial dimensions.

2. A sensing mechanism as defined in claim 1 incl uding means to set thetransducer device to a new zero reference point when wear occurs on thesensing member.

3. A sensing mechanism as defined in claim I wherein said transducerdevice produces a linear output signal.

4. A sensing mechanism as defined in claim 1 wherein said transducerdevice is mounted on a slide movable radially of the abrasive elementfor initial positioning of the sensing member relative to the abrasiveelement.

5. A sensing mechanism as defined in claim 1 wherein said transducerdevice is mounted on a slide movable transversely relative to theabrasive element for sensing changes in the radial dimension thereof atselected points thereacross.

6. In a mechanism for sensing the precise position of a rotatingabrasive element having an operating surface, the abrasive element beingmovable linearly towards or away from a workpiece, the improvementcomprising a hardened sensing pad adapted to continually contact theoperating surface of the abrasive element, the sensing pad forming anextremity of a transducer device set to a zero reference point and beingmovable along a radius of the abrasive element to maintain contacttherewith upon any change in its radial dimensions, the movement of thesensing pad causing a corresponding deviation from the zero referencepoint in the transducer device, and circuit means responsive to suchtransducer deviations to move the abrasive element linearly towards oraway from the workpiece to compensate for the change in radialdimensions, said transducer device being mounted on slide means movabletransversely with respect to the abrasive element operating surface topermit changes in the radial dimensions thereof to be sensed at anydesired point thereacross.

7. A sensing mechanism as defined in claim 5 together with meanscooperable with the sensing pad for setting the transducer device to anew zero reference point when the pad becomes worn.

8. A sensing mechanism as defined in claim 5 wherein said transducerdevice produces a linear output signal.

9. In a mechanism for sensing the precise position of a rotatingabrasive element having an operating surpoint in the transducer device,circuit means responsive to such transducer deviations to move theabrasive element linearly towards or away from the workpiece ,tocompensate for the change in radial dimensions,

means to move the transducer device radially of the abrasive element towithdraw the sensing pad from contact with element operating surface,and normally retracted means movable into the radial path and engageableby the pad, said normally retracted means providing a fixed referencepoint for enabling sensing pad wear to be detected whereby thetransducer device can be set to a new zero reference point to compensatefor the pad wear.

10. A sensing mechanism as defined in claim 8 wherein said transducerdevice produces a linear output signal.

11. A sensing mechanism as defined in claim 8 wherein said transducerdevice and its radial movement means are mounted on a slide movabletransversely to the abrasive element operating surface for sensingchanges in the radial dimension thereof at selected points thereacross.

1. A mechanism for sensing the dimension of a rotating abrasive elementmovable linearly toward and from a workpiece comprising a sensing memberin contact with the abrasive element, the sensing member forming a partof a transducer device initially set to a zero reference point, thesensing member being moved radially of the abrasive element upon anychange in the radial dimension thereof, said movement causing adeviation from the zero reference point in the transducer device,circuit means responsive to the transducer device deviations to move theabrasive element linearly relative to the workpiece to compensate forthe change in radial dimensions.
 2. A sensing mechanism as defined inclaim 1 including means to set the transducer device to a new zeroreference point when wear occurs on the sensing member.
 3. A sensingmechanism as defined in claim 1 wherein said transducer device producesa linear output signal.
 4. A sensing mechanism as defined in claim 1wherein said transducer device is mounted on a slide movable radially ofthe abrasive element for initial positioning of the sensing memberrelative to the abrasive element.
 5. A sensing mechanism as defined inclaim 1 wherein said transducer device is mounted on a slide movabletransversely relative to the abrasive element for sensing changes in theradial dimension thereof at selected points thereacross.
 6. In amechanism for sensing the precise position of a rotating abrasiveelement having an operating surface, the abrasive element being movablelinearly towards or away from a workpiece, the improvement comprising ahardened sensing pad adapted to continually contact the operatingsurface of the abrasive element, the sensing pad forming an extremity ofa transducer device set to a zero reference point and being movablealong a radius of the abrasive element to maintain contact therewithupon any change in its radial dimEnsions, the movement of the sensingpad causing a corresponding deviation from the zero reference point inthe transducer device, and circuit means responsive to such transducerdeviations to move the abrasive element linearly towards or away fromthe workpiece to compensate for the change in radial dimensions, saidtransducer device being mounted on slide means movable transversely withrespect to the abrasive element operating surface to permit changes inthe radial dimensions thereof to be sensed at any desired pointthereacross.
 7. A sensing mechanism as defined in claim 5 together withmeans cooperable with the sensing pad for setting the transducer deviceto a new zero reference point when the pad becomes worn.
 8. A sensingmechanism as defined in claim 5 wherein said transducer device producesa linear output signal.
 9. In a mechanism for sensing the preciseposition of a rotating abrasive element having an operating surface, theabrasive element being movable linearly towards or away from aworkpiece, the improvement comprising a hardened sensing pad adapted tocontinually contact the operating surface of the abrasive element, thesensing pad forming an extremity of a transducer device set to a zeroreference point and being movable along a radius of the abrasive elementto maintain contact therewith upon any change in its radial dimensions,the movement of the sensing pad causing a corresponding deviation fromthe zero reference point in the transducer device, circuit meansresponsive to such transducer deviations to move the abrasive elementlinearly towards or away from the workpiece to compensate for the changein radial dimensions, means to move the transducer device radially ofthe abrasive element to withdraw the sensing pad from contact withelement operating surface, and normally retracted means movable into theradial path and engageable by the pad, said normally retracted meansproviding a fixed reference point for enabling sensing pad wear to bedetected whereby the transducer device can be set to a new zeroreference point to compensate for the pad wear.
 10. A sensing mechanismas defined in claim 8 wherein said transducer device produces a linearoutput signal.
 11. A sensing mechanism as defined in claim 8 whereinsaid transducer device and its radial movement means are mounted on aslide movable transversely to the abrasive element operating surface forsensing changes in the radial dimension thereof at selected pointsthereacross.